JP3310972B1 - Ring-shaped magnet forming apparatus and ring-shaped magnet forming method - Google Patents

Abstract

An object of the present invention is to provide a ring-shaped magnet forming apparatus and a ring-shaped magnet forming method capable of reducing the coaxiality of the ring-shaped magnet and improving the yield and productivity. A ring-shaped magnet forming apparatus includes a die having a through-hole, a core for forming a ring-shaped cavity in the through-hole, and moving along a surface of the die to cut and supply powder into the cavity. It has a feeder box, and upper and lower punches for pressing the powder filled in the cavity to obtain a ring-shaped magnet.
An inclined surface that is inclined in the sliding direction is formed on the distal end surface of the upper punch such that the interval between the distal end surfaces of the upper punch and the lower punch is larger on the rear side than on the front side of the cavity. Alternatively, an inclined surface that is inclined in the sliding direction may be formed on the surface of the die and the core or the tip surface of the lower punch such that the depth on the rear side is smaller than the depth on the front side in the cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring-shaped magnet forming apparatus and a ring-shaped magnet forming method, and more particularly, to a ring-shaped bonded magnet obtained by coating a rare earth alloy powder with a resin binder. The present invention relates to a ring-shaped magnet forming apparatus and a ring-shaped magnet forming method.

[0002]

2. Description of the Related Art In recent years, as the rotation speed of a spindle motor used for a magnetic disk or an optical disk has been increased, there has been a demand for an improvement in the rotational balance of a ring-shaped magnet used for the spindle motor. When molding a ring-shaped magnet,
When the powder is slid into the cavity and fed, the powder is usually filled more strongly toward the rear side of the cavity and the packing density is increased, so that the packing density of the powder in the cavity varies. When the powder is pressed by the upper and lower punches in this state, the core is tilted with respect to the die due to the variation in the packing density of the powder, and a ring-shaped magnet having a different thickness (with uneven thickness) depending on the portion is formed. When such a ring-shaped magnet is used for a spindle motor, the rotational balance of the ring-shaped magnet deteriorates. When the spindle motor is rotated at a high speed, the rotation balance of the ring-shaped magnet is lost even if the difference in the thickness between the portions is small, which is a further problem.

A molding apparatus for suppressing such uneven thickness of a product is proposed in Japanese Patent Application Laid-Open No. 9-241703. Here, the lower end of the core shaft and the upper end of the transmission shaft provided integrally with the core die are connected via a ball joint, and the transmission shaft is positioned in the direction perpendicular to the axis immediately below the connection part by the ball joint. And has a mechanism for guiding the movement in the axial direction. It is stated that the core type can freely tilt about the coupling portion formed by the ball joint with respect to the transmission shaft, so that the eccentricity of the core type and the thickness deviation of the product can be suppressed well.

[0004]

However, according to this prior art, the core shaft becomes long, so that the core mold tends to be eccentric. Therefore, there is a problem that the coaxiality of the obtained ring-shaped magnet is increased, the yield is low, and the productivity is deteriorated. Therefore, the main purpose of this invention is to
An object of the present invention is to provide a ring-shaped magnet forming apparatus and a ring-shaped magnet forming method capable of reducing coaxiality of a ring-shaped magnet, improving yield and improving productivity.

[0005]

According to a first aspect of the present invention, there is provided a ring-shaped magnet forming apparatus for forming a ring-shaped cavity in a through-hole. A core provided, a powder feeding device that moves along the surface of the die and slides and powders the powder into the cavity, and an upper punch and a lower punch that press the powder filled in the cavity to obtain a ring-shaped magnet. The lower punch is characterized in that at least a part of the front end surface of the lower punch has an inclined surface inclined in the sliding direction so that the depth of the rear side of the cavity is smaller than the depth of the front side.

According to a second aspect of the present invention, there is provided a ring-shaped magnet forming apparatus having a die having a through hole, a core provided for forming a ring-shaped cavity in the through hole, and moving along the surface of the die into the cavity. A powder feeding device for slicing and feeding the powder; and an upper punch and a lower punch for pressing the powder filled in the cavity to obtain a ring-shaped magnet. The punch is characterized in that at least a part of the front end surface of the upper punch has an inclined surface inclined in the sliding direction so that the rear side is larger than the front side.

According to a third aspect of the present invention, there is provided the ring-shaped magnet forming apparatus according to the first or second aspect, further comprising a plate for integrally fixing the die and the core. And According to a fourth aspect of the present invention, there is provided the ring-shaped magnet forming apparatus according to any one of the first to third aspects, wherein a height difference of the inclined surface is 0.01 mm or more and 0.15 mm or less. And According to a fifth aspect of the present invention, there is provided a ring-shaped magnet molding apparatus according to any one of the first to fourth aspects, wherein the powder is a powder for a bonded magnet obtained by coating a rare earth alloy powder with a resin binder. It is characterized by.

According to a sixth aspect of the present invention, there is provided a ring-shaped magnet forming method, wherein powder is slid and cut into a ring-shaped cavity formed by using a die having a through hole and a core, and the powder is pressed to form a ring. A ring-shaped magnet forming method for forming a magnet, wherein at the time of powder feeding, at least a part of a front end surface of a lower punch is provided with an inclined surface so that a depth of a rear side is made shallower than a depth of a front side in a cavity. Thus, the powder is slid into the cavity and fed.

According to a seventh aspect of the present invention, there is provided a ring-shaped magnet forming method, wherein powder is slid and cut into a ring-shaped cavity formed by using a die having a through hole and a core, and the powder is pressed by a pair of punches. A ring-shaped magnet forming method for forming a ring-shaped magnet, wherein the interval between the tip surfaces of a pair of punches at the time of forming is larger on the rear side than on the front side of the cavity with respect to the feeding direction of the powder feeding device. It is characterized by the following.

According to an eighth aspect of the present invention, there is provided a ring-shaped magnet forming method according to the sixth or seventh aspect, wherein the die and the core are integrally fixed via a plate. I do. A ring magnet molding method according to a ninth aspect is the ring magnet molding method according to any one of the sixth to eighth aspects, wherein the difference in the depth of the cavity or the maximum difference in the interval between the tip end surfaces of the pair of punches. Is 0.01
mm or more and 0.15 mm or less.

According to a tenth aspect of the present invention, there is provided a method for forming a ring magnet according to any one of the sixth to ninth aspects, wherein the powder comprises a rare earth alloy powder coated with a resin binder. It is characterized by being.

[0012] In the ring-shaped magnet forming apparatus according to the first aspect, at least a part of the tip end surface of the lower punch is inclined in accordance with the filling variation due to the sliding cutting powder supply, so that the depth of the rear side of the cavity is adjusted to the front side. Shallower than the side depth. As a result, even in the case of powdering by grinding, the filling amount of each part in the cavity, particularly the rear side and the front side, is substantially equal, or the filling amount of the front side is increased. Then
When the powder in the cavity is pressed, the difference in molding pressure applied to the powder in the cavity can be reduced, so that the eccentricity of the core with respect to the die can be suppressed, and a ring-shaped magnet with a small variation in molding density can be obtained. Therefore, the coaxiality of the ring-shaped magnet is reduced, the yield is improved, and the productivity can be increased. The same applies to the ring-shaped magnet forming method according to the sixth aspect.

[0013] In the ring-shaped magnet forming apparatus according to the second aspect, at least a part of the upper punch is tilted in accordance with the filling variation due to the sliding cutting and feeding, and the tip surfaces of the upper punch and the lower punch at the time of forming are formed. The interval is larger on the rear side than on the front side of the cavity with respect to the direction of the powder feeding device. Therefore, when powder is pressed in the cavity, the volume of the cavity is larger than that of the front side, despite the fact that the filling density is higher on the rear side than on the front side of the cavity with respect to the feeding direction of the powder feeding device due to the sliding-off powder supply. Since the size of the rear side can be increased, the difference in molding pressure applied to the powder in the cavity can be reduced. Therefore, eccentricity of the core with respect to the die can be suppressed, and variation in the molding density of the obtained ring-shaped magnet can be reduced. As a result, the coaxiality of the ring-shaped magnet is reduced, the yield is improved, and the productivity can be increased. The same applies to the ring-shaped magnet forming method according to the seventh aspect.

According to a third aspect of the present invention, the core can be strongly fixed by integrally fixing the die and the core via the plate, so that the core can be further prevented from being blurred in the through hole. The coaxiality of the ring magnet is further reduced. The same applies to the ring-shaped magnet forming method according to the eighth aspect. When the height difference of the inclined surface is 0.01 mm or more and 0.15 mm or less as described in claim 4, it is possible to appropriately offset the variation in the filling of the powder filled in the cavity. Therefore, it is possible to reduce the variation in the molding density of the obtained ring-shaped magnet, and to obtain a high-quality ring-shaped magnet with small coaxiality. As described in claim 9, the difference between the depth of the cavity and the maximum difference between the tip surfaces of the pair of punches is not less than 0.01 mm and not more than 0.15 m.
The same applies to the case of m or less.

The present invention is particularly effective when pressing, for example, a bonded magnet powder in which a resin binder is mixed into a rare earth alloy powder as described in claim 5. Such a powder for bonded magnets has poor fluidity and must be pressed at a high pressure during magnet molding. In the past, the core was easily tilted due to the high pressure applied to the powder in addition to the variation in powder filling. However, according to the present invention, even with such a powder, variation in filling can be suppressed and inclination of the core can be prevented. The same applies to the ring-shaped magnet forming method according to the tenth aspect.

In this specification, the terms "front side" and "rear side" of a cavity refer to a front part and a front part of a cavity, respectively, when a powder feeding device such as a feeder box enters the cavity. Refers to the rear. "Coaxiality" refers to "JIS B0021 Appendix 1
"1.1 Coaxiality tolerance" indicates a difference between an ideal diameter centered on a reference axis having an arbitrary axis length and an actually manufactured diameter. The numerical value is represented by twice the distance between the ideal center and the actual center.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 1, a ring-shaped magnet forming apparatus 10 according to one embodiment of the present invention is a die float type forming apparatus, and includes a press frame 12.
In the press frame 12, a die 1 integrated with a die and a core is provided.
4 are arranged.

As shown in FIGS. 2 to 4, the mold 14 includes a substantially cylindrical die 16. The die 16 has a through hole 18 having a circular cross section, a hollow portion 20 having a diameter larger than the through hole 18 and communicating with the through hole 18, and a step portion 22 formed below the hollow portion 20. A plurality of (four in this embodiment) holes 24 are formed in the lower surface of the die 16 at equal intervals in the vertical direction, and a plurality of (eight in this embodiment) holes are formed in the lower part of the outer surface of the die 16. Alignment holes 26 are formed at substantially equal intervals and in the center direction.

Such a die 16 is arranged on a disk-shaped die lower plate 28. Die lower plate 28 has holes 3 at positions corresponding to holes 24 of die 16 respectively.
0 is formed, and a substantially fan-shaped hole 32 is formed slightly inside each hole 30. A bearing member (slide guide member) 34 having a surface substantially flush with the inner side surface of the hole 32 is provided below the hole 32. The lower punch holder 66 (described later) is guided by the bearing member 34 to improve the overall accuracy at the time of assembly. Die 16 and die lower plate 28 are integrally fixed by screws 36 inserted into holes 24 and 30.

A core 38 is disposed on the die lower plate 28 and in the cavity 20 of the die 16. The core 38 includes a disk-shaped flange portion 40, and the flange portion 40 has a die lower plate 2.
8 are substantially fan-shaped holes 42 at positions corresponding to the respective holes 32.
Is formed. The core 38 is fixed by sandwiching the flange 40 of the core 38 between the upper surface of the die lower plate 28 and the step 22 of the die 16, and the upper end surface of the core 38 and the upper surface of the die 16 are substantially flush. .

The core 38 is centered by a centering screw 44 formed of, for example, a hexagonal screw and screwed into the hole 26 of the die 16, and a locking screw 46 is attached to the head of the centering screw 44. By screwing in, the horizontal position of the core 38 is fixed. An annular lower punch washer 48 and a substantially cylindrical lower punch 50 are provided on the flange 40 of the core 38.
And an annular lower punch presser foot 52 are sequentially arranged. The lower punch washer 48 has a hole 5 for fixing the lower punch holder 66.
4 and holes 56 for fixing the lower punch presser 52 are formed alternately and plurally (four each in this embodiment). A step portion 58 is formed at the lower portion of the outer surface of the lower punch 50, and the distal end surface of the lower punch 50 moves in a retreating direction, that is, a sliding direction of a feeder box 116 (described later) indicated by an arrow e as shown in FIG. Inclined slope 50a
Is formed as The height difference L of the inclined surface 50a of the lower punch 50 is set to, for example, 30 μm. In this case, the maximum difference in depth between the front side 65b and the rear side 65a of the cavity 65 described later is also 30 μm. Lower punch foot 52
A hole 60 is formed at a position corresponding to each hole 56 of the lower punch washer 48, and a step portion 62 is formed below the inner surface of the lower punch presser foot 52.

The lower punch 50 is sandwiched between the lower punch washer 48 and the lower punch presser foot 52 and is fixed by screws 64 inserted into the holes 56 and 60. At this time, the lower punch washer 48, the lower punch 50, and the lower punch presser 5
2 is housed in the cavity 20 of the die 16 and the lower punch 5
The upper part of 0 is exposed in the through hole 18. Thus, in the through hole 18 of the die 16, the die 16 and the core 3
8 and the inclined surface 50 a of the lower punch 50 form an annular cavity 65. The cavity 65 is
The inclined surface 50a of the lower punch 50 becomes shallower in the sliding direction of the feeder box 116, and the depth of the rear side 65a in the cavity 65 is made shallower than the depth of the front side 65b.

A lower punch holder 66 is attached to the lower surface of the lower punch washer 48. Lower punch holder 66
Has four shaft portions 68 having a substantially fan-shaped cross section which are inserted into the holes 32 of the die lower plate 28 and the holes 42 of the core 38, and each shaft portion 68 has a hole 5 of the lower punch washer 48.
4, a through hole 70 is formed. And
The shaft portion 68 of the lower punch holder 66 has the holes 32 and 4
The lower punch holder 66 and the lower punch washer 4 are inserted by inserting the screw 72 into the holes 70 and 54.
8 are integrated.

Returning to FIG. 1, the lower punch holder 66 of the mold 14 formed in this manner is a lower punch holder washer 74.
The lower punch holder presser foot 76 holds the lower portion of the lower punch holder 66, and the screw 78 is inserted into the lower punch holder presser 76 and the lower punch holder washer 74, thereby lowering the lower punch holder 66. It is fixed on the punch holder washer 74. Lower punch holder washer 74
Are placed on a base plate 82 supported by legs 80 in the press frame 12 and secured by screws 84. Thus, the lower punch 50 is fixed. A through hole 86 is formed in the base plate 82, and a guide bush 88 is provided in the through hole 86.

The die 16 is held by a dilator 90 and a die presser 92, and is fixed by inserting a screw 94 into the die presser 92 and the diretina 90. The lower surface of the diritina 90 is connected to a lower connecting base 98 via a pole 96, and the lower connecting base 98 is connected to a press lower ram 100. By moving the press lower ram 100 up and down, the die 16 and the core 38 can be moved up and down, and die floating is possible.

An upper punch guide post 102 is provided upright on the upper surface of the dilator 29, and the upper punch guide post 102 guides the upper punch plate 104 in the vertical direction. An upper punch 110 is held on the lower surface of the upper punch plate 104 by an upper punch washer 106 and an upper punch presser foot 108.
Is fixed to the upper punch washer 106 and the upper punch presser foot 108. A press upper ram 114 is connected to the upper surface of the upper punch plate 104, and the upper punch 110 can be moved up and down by moving the press upper ram 114 up and down.
10 can move into and out of the cavity 65.

In the vicinity of the press frame 12, the feeder box 11 can move forward and backward with respect to the cavity 65.
6 are arranged. The powder 118 supplied to the cavity 65 is stored in the feeder box 116. The powder 118 is, for example, a powder for a bonded magnet in which a rare earth alloy powder is coated with a resin binder. For example, by mixing and drying an epoxy resin or the like having a weight ratio of about 1% to 5% with respect to the MQP-B magnet powder manufactured by MQI Co., Ltd., a resin-coated bond magnet powder can be produced. (For example, JP-A-2000-119702). The particle size of the compound is between 30 μm and 250 μm.

Core 3 in ring-shaped magnet forming apparatus 10
The operation at the time of centering of No. 8 will be described. With the lower punch 50, the core 38, etc. built into the die 16, the screws 36 are tightened to the extent that the core 38 can be aligned.
The die 16 is fixed in advance. At this time, the core 38 is disposed on the die lower plate 28.

Then, the alignment screws 44 screwed into the holes 26 of the die 16 are lightly tightened one by one over the entire circumference, and the adjustment gap G is measured with a pin gauge (not shown). . As a result of measuring the gap G over the entire circumference, if the (maximum value−minimum value) of the gap G exceeds 5 μm, the centering screw 44 in the small portion of the gap G is loosened, and the adjustment of the portion in the large portion of the gap G is performed. The core screw 44 is further tightened so that the (maximum value−minimum value) of the gap G is adjusted to 5 μm or less. After the core 38 is thus aligned, the screw 36 is further tightened to integrate the die 16, the die lower plate 28, and the core 38.

In this embodiment, when the outer diameter X of the die 16 is about 120 mm, the length L of the core 38 is set to about 75 mm. The clearance between the die 16 and the lower punch 50 and the clearance between the core 38 and the lower punch 50 are set to 5 μm to 10 μm.

The operation of the ring-shaped magnet forming apparatus 10 will be described. First, the cavity 16 is formed by raising the die 16 and the core 38. Then, the feeder box 116 is advanced toward the die 16 in a direction exactly opposite to the sliding direction indicated by the arrow e in FIG. At this time, the powder 118 in the feeder box 116 is dropped into the cavity 65 by gravity. When the filling is completed, the feeder box 116 retreats in the direction opposite to the entering direction (sliding direction), and excess powder is scraped off by the bottom edge of the feeder box 116. At this time, the powder is supplied in a state where the depth of the rear side 65a in the cavity 65 is smaller than the depth of the front side 65b.

Next, the upper punch 110 is inserted into the cavity 65.
, And the powder 118 in the cavity 65 is press-molded. At this time, the powder 1 in the cavity 65
18 is compressed by the upper punch 110 and the lower punch 50, but the pressing force against the powder 118 is usually 500 MPa.
It is not less than 1500 MPa. A pair of upper and lower punches 11
If the pressing force at 0,50 is less than 500 MPa, desired magnetic characteristics cannot be obtained in the obtained ring-shaped magnet 120 (see FIG. 6). On the other hand, when the pressing force is 150
If the pressure exceeds 0 MPa, the force applied to the die 16 and the core 38 becomes too large, and the mold 14 may be damaged. The pressing force by the pair of upper and lower punches 110 and 50 is set to 50
When the pressure is 0 MPa or more and 1500 MPa or less, the above-mentioned adverse effects can be suppressed. The more preferable range of the pressing force is 7
It is not less than 00 MPa and not more than 1300 MPa. In this embodiment, it is set to 1200 MPa. Then, after raising the upper punch 110, the die 16 and the core 38 are lowered, and the obtained ring-shaped magnet 120 is exposed on the die 16 and taken out.

According to the ring-shaped magnet molding apparatus 10, since the inclined surface 50a of the lower punch 50 is inclined upward in the sliding direction indicated by the arrow e, the depth of the rear side 65a in the cavity 65 is smaller than that of the front side 65b. Shallower than depth.
For this reason, the powder 118 is generally located closer to the rear side of the cavity 65.
Are filled strongly, and the packing density is increased.
The filling amount of the powder 118 into the front side 65b of the
Can be larger than the filling amount of the powder 118 into the container. Therefore,
The difference in molding pressure between the portions in the cavity 65 can be reduced, the molding density of the ring magnet 120 obtained by pressing the powder 118 in the cavity 65 can be made substantially uniform, and the annular ring magnet 120 having a small coaxiality can be obtained. Can be obtained, and the yield and productivity of the ring-shaped magnet 120 can be improved.

Also, by fixing the die 16 and the core 38 integrally on the die lower plate 28, the core 3
8 can be firmly fixed, and the positional relationship between the die 16 and the core 38 can be stabilized so that the core 38 does not become eccentric with respect to the die 16. Further, since the core 38 can be shortened (75 mm in this embodiment), the assembling of the mold 14 becomes easy, and the assembling accuracy can be stabilized without much skill. Further, if the pressing force by the upper punch 110 and the lower punch 50 is set to 500 MPa or more and 1500 MPa or less, the ring-shaped magnet 120 having desired magnetic characteristics can be obtained, and the mold 14 can be prevented from being damaged.

According to the ring-shaped magnet molding apparatus 10, even when the powder for bonded magnets in which the rare earth alloy powder is coated with the resin binder is used, the variation in filling can be suppressed, and the inclination of the core 38 can be prevented. The present invention is particularly effective when the thickness of the ring-shaped magnet 120 is 2.5 mm or less. If the thickness of the ring-shaped magnet 120 to be manufactured is small, the ring-shaped magnet 12
This is because the eccentricity of 0 becomes large.

Another embodiment will be described with reference to FIG. In this embodiment, the mold 14 includes a lower punch 50.
And a horizontal tip surface 122a instead of the upper punch 110
, And an upper punch 124 having an inclined surface 124a facing the distal end surface 122a. The inclined surface 124a is inclined such that the distance between the inclined surface 124a and the leading end surface 122a increases in the sliding direction of the feeder box 116 indicated by an arrow e. The height difference M of the inclined surface 124a is
For example, it is set to 60 μm. In this case, upper punch 1
The maximum difference in the distance between the inclined surface 124a, which is the distal end surface of the lower punch 24, and the distal end surface 122a of the lower punch 122 is also 60 μm.

In this manner, by inclining the tip surface of the upper punch 124, the upper and lower punches 12 during molding can be formed.
The interval between the tip surfaces of the 4,122 is made larger on the rear side 65a than on the front side 65b of the cavity 65, so that the volume at the time of pressing the portion where the filling amount is large is increased.

According to this embodiment, even if the filling density is higher on the rear side 65a of the cavity 65, the space between the front end surface 122a and the inclined surface 124a during molding, and consequently, the volume is larger on the rear side 65a of the cavity 65. In addition, the difference in molding pressure between the portions in the cavity 65 can be reduced, and the molding density of the ring-shaped magnet 120 becomes substantially uniform. Therefore, a high-quality annular ring-shaped magnet 12 having a small coaxiality
0 can be obtained, and the yield and productivity of the ring-shaped magnet 120 can be improved. Further, in this embodiment, even if the height dimension of the ring-shaped magnet 120 to be formed is changed, it can be easily dealt with only by replacing the upper punch 124.

Another embodiment will be described with reference to FIGS. In this embodiment, a die 126 is used instead of the die 16, and a core 127 is used instead of the core 38. The cavity 6 in the upper surface of the die 126
5, an inclined surface 126a is formed. Slope 12
6a is inclined downward in the sliding direction of the feeder box 116 indicated by the arrow e. Thereby, the cavity 6
5, the rear side 65a is shallower than the front side 65b with respect to the feeder box 116 approaching direction, and the height difference N
Is set to, for example, 30 μm. In this case, the maximum difference between the depth of the front side 65b and the rear side 65a of the cavity 65 is also 30 μm. The upper surface of the core 127 is
6 becomes an inclined surface 127a that is inclined so as to be included in the same plane as the inclined surface 126a. Tip surface 12 of lower punch 122
2a and the tip surface 110a of the upper punch 110 are formed horizontally without being inclined. In this embodiment, at the time of powder supply, powder is supplied in a state where the depth of the rear side 65a of the cavity 65 is smaller than the depth of the front side 65b.

According to this embodiment, even if the packing density is higher on the rear side 65a of the cavity 65, the cavity 118 is shallower on the rear side 65a. Thus, the difference in molding pressure between the portions in the cavity 65 can be reduced, and the molding density becomes substantially uniform. Therefore, a high-quality annular ring magnet 120 having a small coaxiality can be obtained, and the yield and productivity of the ring magnet 120 can be improved.

Another embodiment will be described with reference to FIG. In this embodiment, the mold 14 is
It includes a lower punch 128 used in place of the lower punch 50, and an upper punch 110 having a horizontal tip surface 110a.
The tip surface of the lower punch 128 has an inclined surface 1 that is inclined upward in the sliding direction of the feeder box 116 indicated by an arrow e.
28a and a horizontal plane 128b are formed. Horizontal plane 12
8b, the feeder box 11 is larger than the inclined surface 128a.
6 is provided on the sliding direction side. The inclined surface 128a and the horizontal surface 128b are formed, for example, such that the areas thereof are substantially equal. The height difference S of the inclined surface 128a is set to, for example, 30 μm. In this case, the cavity 65
The maximum difference in depth between the front side 65b and the rear side 65a is also 30μ.
m.

According to this embodiment, even if the packing density of the powder 118 becomes higher toward the rear side 65a of the cavity 65, the cavity 65 becomes deeper toward the front side 65a.
The filling amount of the powder 118 into the front side 65b of the cavity 65 can be larger than the filling amount into the rear side 65a. Therefore, similarly to the embodiment shown in FIG. 5, an annular ring-shaped magnet 120 having small coaxiality can be obtained, and the yield and productivity of the ring-shaped magnet 120 can be improved.

Another embodiment will be described with reference to FIG. In this embodiment, the mold 14 is
An upper punch 130 used in place of the upper punch 110,
A lower punch 122 having a horizontal tip surface 122a. An inclined surface 130a and a horizontal surface 130b are formed on the distal end surface of the upper punch 130. The inclined surface 130a is formed by a feeder box 11 indicated by an arrow e more than the horizontal surface 130b.
6, and is inclined so that the distance from the tip surface 122a increases toward the sliding direction of the feeder box 116. The height difference T of the inclined surface 130a is set to, for example, 30 μm. In this case, the tip surface of the upper punch 130 and the tip surface 122a of the lower punch 122
Is also 30 μm. Slope 130a
The horizontal plane 130b is formed, for example, so that the areas thereof are substantially equal to each other.

According to this embodiment, even if the filling density of the powder 118 becomes higher toward the rear side 65 a of the cavity 65, the tip surface of the upper punch 130 and the lower punch 122
Of the cavity 65 on the rear side 6 of the cavity 65.
Since it is as large as 5a, similarly to the embodiment shown in FIGS. 8 and 9, the molding density becomes substantially uniform. Therefore, a high-quality annular ring magnet 120 having a small coaxiality can be obtained, and the yield and productivity of the ring magnet 120 can be improved.

The height differences L, M, N, S and T are
For example, when a ring-shaped magnet for a spindle motor is manufactured, the diameter is preferably 0.01 mm or more and 0.15 mm or less. Within this range, variations in the filling of the powder 118 into the cavity 65 can be offset, and the ring-shaped magnet 12
Although the molding density of 0 can be made substantially uniform, if it exceeds this range, the filling variation will occur. More preferably, the range of the height differences L, M, N, S and T is 30 μm
９０90 μm. The ranges of the height differences L, M, N, S and T can be appropriately changed according to the size of the ring-shaped magnet 120 to be obtained. The area of the inclined surface 128a and the horizontal surface 128
The ratio of the area b to the area and the ratio of the area of the inclined surface 130a to the area of the horizontal plane 130b are 1 to 1 in the above-described embodiment, but are not limited thereto.

Next, when the upper punch 124 having the inclined surface 124a is used for the mold 14 in which the die 16 and the core 38 are integrally fixed (hereinafter referred to as "the inclined upper punch integrated mold").
) And a case where the lower punch 50 having the inclined surface 50a is used in a conventional mold in which a die and a core are separated (hereinafter, referred to as a die).
A ring-shaped magnet was formed for each of a conventional die having a conventional punch having no tilt and a conventional punch having no tilt (hereinafter referred to as a conventional die having no tilt). The result is shown in FIG. In this experiment, the concentricity was obtained for the obtained 1000 ring-shaped magnets. The dimensions of the ring-shaped magnet were 31 mm outside diameter, 28.4 mm inside diameter, 3.9 mm height, and 1.3 mm thickness = (outside diameter−inside diameter) ÷ 2.

As can be seen from FIG. 12, the concentricity of the conventional mold having no inclination exceeds 20 μm in most cases, whereas the concentricity of the conventional mold having the inclined punch has the concentricity of 20 μm.
It can be seen that the coaxiality can be improved by using the lower punch 50 having the inclined surface 50a. Further, according to the inclined upper punch integrated mold, the coaxiality can be suppressed to 8 μm or less in most cases.
And the core 38 are integrally fixed to the mold 14 with the inclined surface 1.
It is understood that the use of the upper punch 124 having 24a can further greatly improve the coaxiality.

The ring-shaped magnet 1 obtained according to the present invention
20 can be used for a spindle motor 200 as shown in FIG. 13, for example. Spindle motor 200
Is a fixed frame 202 attached to the magnetic disk drive C, and a rotor 208 rotatably connected to the fixed frame 202 via a pair of bearings 204 and 206.
The disk D is mounted on the rotor 208.
The rotor 208 is rotated by the magnetic action of the armature 210 provided on the fixed frame 202 and the ring-shaped magnet 120 provided on the inner periphery of the rotor 208.

When the ring-shaped magnet 120 with improved coaxiality is used for the spindle motor 200, the ring-shaped magnet 12
The rotation balance of 0 is stabilized. Therefore, even if the spindle motor 200 is used for a hard disk drive that requires a rotation speed of, for example, about 10,000 rpm,
Operation can be stabilized. The inclined surface may be formed on at least one of the die and the core, the upper punch, and the lower punch.

[0050]

According to the present invention, a high quality ring-shaped magnet having a small coaxiality can be obtained, and the yield and productivity of the ring-shaped magnet can be improved.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2A is a cross-sectional view illustrating a mold, and FIG. 2B is a view illustrating an A-A cross section thereof.

FIG. 3 is a perspective view when a mold is cut in a vertical direction.

FIG. 4 is an exploded perspective view when the mold is cut in a vertical direction.

FIG. 5 is an illustrative sectional view showing a main part of the embodiment of FIG. 1;

FIG. 6 is a perspective view showing an example of a ring-shaped magnet.

FIG. 7 is an illustrative sectional view showing a main part of another embodiment.

FIG. 8 is a perspective view showing a main part of another embodiment.

FIG. 9 is an illustrative sectional view showing a main part of the embodiment shown in FIG. 8;

FIG. 10 is an illustrative sectional view showing a main part of still another embodiment.

FIG. 11 is an illustrative sectional view showing a main part of still another embodiment.

FIG. 12 is a graph showing experimental results.

FIG. 13 is a sectional view showing an example of a spindle motor using a ring-shaped magnet.

[Explanation of symbols]

Reference Signs List 10 ring-shaped magnet forming apparatus 14 mold 16, 126 die 18 through hole 28 die lower plate 38, 127 core 50, 122, 128 lower punch 50a, 124a, 126a, 127a, 128a, 1
30a Inclined surface 65 Cavity 65a Back side of cavity 65b Front side of cavity 110, 124, 130 Upper punch 110a, 122a Tip surface 116 Feeder box 118 Powder 120 Ring magnet 128b, 130b Horizontal plane e Feeder box sliding direction L, M , N, S, T Height difference of slope

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-236205 (JP, A) JP-A-2000-119702 (JP, A) JP-A-2000-188462 (JP, A) JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B30B 11/00 B30B 11/02 B22F 3/02 B22F 3/035

Claims (10)

(57) [Claims] A die having a through-hole; a core provided to form a ring-shaped cavity in the through-hole; and a supply for moving along the surface of the die and sliding and powdering the powder into the cavity. A powder device, and an upper punch and a lower punch for pressing the powder filled in the cavity to obtain a ring-shaped magnet, such that a depth on a rear side is smaller than a depth on a front side in the cavity. A ring-shaped magnet forming apparatus having at least a part of a tip surface of the lower punch having an inclined surface inclined in the sliding direction. 2. A die having a through-hole, a core provided to form a ring-shaped cavity in the through-hole, and a supply for moving along the surface of the die and sliding and powdering the powder into the cavity. A powder device, and an upper punch and a lower punch for pressing the powder filled in the cavity to obtain a ring-shaped magnet, wherein a distance between tip surfaces of the upper punch and the lower punch is a front side of the cavity. A ring-shaped magnet forming apparatus, wherein at least a part of a tip end surface of the upper punch has an inclined surface inclined in the sliding direction so that the rear side becomes larger. 3. The ring-shaped magnet forming apparatus according to claim 1, further comprising a plate for integrally fixing the die and the core. 4. The ring-shaped magnet forming apparatus according to claim 1, wherein a height difference of the inclined surface is 0.01 mm or more and 0.15 mm or less. 5. The ring-shaped magnet molding apparatus according to claim 1, wherein the powder is a bonded magnet powder obtained by coating a rare earth alloy powder with a resin binder. 6. A ring-shaped magnet forming method in which powder is slid and cut into a ring-shaped cavity formed by using a die and a core having a through-hole, and the powder is pressed to form a ring-shaped magnet. At the time of powder feeding, the powder is placed in the cavity in a state where the rear side depth is made shallower than the front side depth in the cavity by providing an inclined surface at least at a part of the front end surface of the lower punch. A ring-shaped magnet molding method for grinding and feeding. 7. A ring-shape in which powder is slid and cut into a ring-shaped cavity formed by using a die and a core having a through hole, and the powder is pressed by a pair of punches to form a ring-shaped magnet. A magnet forming method, wherein a distance between tip surfaces of the pair of punches at the time of molding is larger on a rear side than on a front side of the cavity. 8. The method according to claim 6, wherein the die and the core are integrally fixed via a plate. 9. The difference between the depth of the cavity or the maximum difference between the tip surfaces of the pair of punches is 0.01 mm.
The method for forming a ring-shaped magnet according to any one of claims 6 to 8, which is not less than 0.15 mm. 10. The ring-shaped magnet molding method according to claim 6, wherein the powder is a powder for a bonded magnet in which a rare earth alloy powder is coated with a resin binder.